Mechanism Of Damage Formation Research Articles

Liquid water radiolysis induced by secondary electrons generated from MeV-energy carbon ions.

Fast ion beams induce damage to deoxyribonucleic acid (DNA) by chemical products, including secondary electrons, produced from interaction with liquid water in living cells. However, the production process of these chemical products in the Bragg peak region used in particle therapy is not fully understood. To investigate this process, we conducted experiments to evaluate the radiolytic yields produced when a liquid water jet in vacuum is irradiated with MeV-energy carbon beams. We used secondary ion mass spectrometry to measure the products, such as hydronium cations (H3O+) and hydroxyl anions (OH-), produced along with ·OH radicals, which are significant inducers of DNA damage formation. In addition, we simulated the ionization process in liquid water by incident ions and secondary electrons using a Monte Carlo code for radiation transport. Our results showed that secondary electrons, rather than incident ions, are the primary cause of ionization in water. We found that the production yield of H3O+ or OH- was linked to the frequency of ionization by secondary electrons in water, with these electrons having energies between 10.9 and 550eV. These electrons are responsible for ionizing the outer-shell electrons of water molecules. Finally, we present that the elementary processes contribute to advancing radiation biophysics and biochemistry, which study the formation mechanism of DNA damage.

Machining damage in the fabrication of polycrystalline diamond micro end mill with laser and grinding combined processing method

The high hardness and wear resistance of polycrystalline diamond (PCD) micro tool make it widely used in precision machining of small parts of difficult-to-machine materials. The laser and grinding combined machining is an effective method to fabricate PCD micro tools, but the machining damage is difficult to control, which will reduce the cutting performance and tool life. Therefore, this paper aims to deeply study the damage forms and damage formation mechanisms during the fabrication process of PCD micro end mills, so as to improve the quality of the PCD micro mills. The laser and grinding combined machining experiments of PCD micro end mill are carried out, and the surface morphology characteristics and cutting edge of the mill are observed and analyzed. The influence of process parameters on the fabrication quality of PCD micro mill is investigated. The experimental results show that the high temperature of the laser is the main factor causing damage, which causes the melting and oxidation of the surface material, and further forms micro cracks, pits and oxidized attachments on the PCD mill. In addition, diamond phase transformation and excessive removal of cobalt-rich layer will also lead to graphitization and micro-grooves on the mill surface. For the grinding process, the cutting edge is fractured by the impact of the wheel, resulting in micro notches, micro pits and micro cracks. The intergranular crack expansion of PCD material and cleavage breakage of diamond particles are the main causes of micro cracks and micro pits on the mill surface. In addition, the chips will also scratch the tool surface to produce micro nicks and cause the chips coating on the rake face. The research results are helpful to further understand the damage mechanism of laser and grinding combined machining PCD mill, so as to improve the fabrication quality of micro tools.

Study of damage mechanism on single crystal 4H-SiC surface layer by picosecond laser modification (PLM)

The stable structure, high hardness, and brittleness of single-crystal 4H-SiC present challenges in achieving efficient and damage-free polishing processing. Ultra-short pulsed laser-induced surface modification provides a new solution to enhance the manufacturability of 4H-SiC. This paper aims to investigate the underlying mechanism of the picosecond laser-induced surface structural changes in 4H-SiC and the process of material removal from solid to vapour, elucidating the interaction mechanism between picosecond laser and 4H-SiC. A temperature gradient distribution model for picosecond laser irradiation on 4H-SiC was built to reveal the formation mechanism of subsurface crack damage. The results show that a combination of phase explosion and thermal effects controlled picosecond laser-modified 4H-SiC surfaces deposited spherical SiO2 particles and the process. The study demonstrates that the cracking behaviour in the subsurface of picosecond laser-modified SiC predominantly occurs in the recast region. The fundamental cause of cracking is attributed to the tensile stresses generated by thermal effects and the volumetric changes in the molten material resulting from the overlapping of neighbouring spots in alternating hot–cold cycles. The nanoindentation demonstrated that laser modification can effectively enhance the machinability of SiC. The findings of this study can provide a theoretical basis for efficient non-destructive machining of hard and brittle materials.

Effect of bridge height on airflow and aeolian sand flux near surface along the Qinghai-Tibet Railway, China

In this work, we studied the near-surface flow field structure of railway bridges with different heights through field investigation and wind tunnel simulation experiments. Meanwhile, we simulated the distribution of sand accumulation around a bridge via CFD software based on the sand accumulation around the Basuoqu bridge in the Cuona Lake section of the Qinghai–Tibet Railway. Results show that the sand around this railway bridge is mainly from the lake sediment on the west side of the railway and the weathered detritus on the east side. The height of the railway bridge in the sandy area affects the distribution of the near-surface flow field and the variation in speed on both sides of the bridge. The wind speed trough on both sides of the 6 m high bridge is higher, and the horizontal distance between the wind speed trough and the bridge section is 1.5 times that of the 3 m high bridge. Wind speed attenuates in a certain range on the windward and leeward sides of the bridge, forming an aeolian area; under the beam body, it is affected by the narrow tube effect, forming a wind erosion area. The height of the bridge determines its sand transport capacity. Under certain wind conditions, the overhead area at the bottom of the 3 m high bridge and its two sides do not have the sand transport capacity, so sand accumulates easily. Nevertheless, the sand accumulation phenomenon gradually disappears with the increase in bridge clearance height. The objectives of this study are to reveal the formation mechanism of sand damage for railway bridges, provide theoretical support for the scientific design of railway bridges in sandy areas, and formulate reasonable railway sand prevention measures to ensure the safety of railway running, which have certain theoretical significance and practical value.

Unveiling damage mechanisms of SiC fiber-reinforced titanium matrix composites through ultrasonic scratching

SiCf/Ti composites are increasingly being utilized in the aerospace field due to their excellent performance. However, during the application of this material, issues such as fiber fracture and debonding often occur during processing. Ultrasonic vibration-assisted machining technology avoids the waste of cutting fluid and its environmental impact in traditional production, making it widely used in the ultra-precision and environmentally friendly processing of composite materials. This study explores the damage formation mechanism during material removal using diamond scratching. A comparison was made between the specific energy and morphology of ultrasonic scratching and conventional scratching, and a model for fiber fracture depth was established. The results indicate that conventional cutting leads to fiber bending and crushing, with bent fibers causing deformation to the matrix, which further affects the fibers behind. EBSD results confirm that fiber bending deformation affects the microstructure changes in the matrix. Under ultrasonic scratching, scratching force and specific energy decreased by 25% and 50%, respectively, compared to conventional scratching. This effectively reduces the deformation of fibers on the matrix during cutting and enhances the tool's ability to shear and remove fibers. CT analysis of the subsurface showed that under ultrasonic scratching, the maximum decrease in fiber fracture depth was 13% compared to traditional methods. This study guides the clean and low-damage machining of SiCf/Ti composites.

Analysis of thermal damage formation and extension mechanism in CFRP short pulse laser cutting based on an inhomogeneous mesoscopic ablation model

Analysis of thermal damage formation and extension mechanism in CFRP short pulse laser cutting based on an inhomogeneous mesoscopic ablation model

Study on the atomic removal behavior and damage formation mechanism of nano cutting copper–nickel alloy with diamond tool

The effects of tool rake angle and cutting depth on cutting temperature, cutting force, friction coefficient of rake tool face, atomic accumulation of chip flow and removal, surface quality, sub-surface damage layer thickness, atomic stress, and dislocation evolution were studied by molecular dynamics simulations. The results showed that the cutting temperature was concentrated on the chip, and the chip was easy to flow out with the increase of the tool rake angle, which weakens the extrusion and shearing action of the workpiece, resulting in the gradual reduction of tangential force. The tool rake angle of 10° is beneficial to improve the surface/subsurface quality of the workpiece. The minimum root-mean-square roughness obtained was 0.73 Å. The atomic stress of the workpiece was mainly concentrated around the area of interaction with the tool, and the atoms on the finished surface underwent elastic recovery, so the atomic stress was not significant. The 1/6<112> (Shockley) dislocation density had always been in the leading position, and 1/6<112> (Shockley) dislocation was continuously synthesized and decomposed during the nano-cutting process. With the increase of cutting depth, the number of atoms removed increases rapidly, and the width of chip side flow increases, but the symmetry is weakened. The contour line map even shows deep wave valleys caused by the absence of atoms, which increases the surface roughness. Moreover, the area and depth of the atomic stress distribution in the subsurface layer increase, and the number of amorphous atoms and dislocation density increase.

Characterization, quantitative evaluation, and formation mechanism of surface damage in ultrasonic vibration assisted scratching of Cf/SiC composites

Carbon fiber reinforced silicon carbide ceramic matrix composites (Cf/SiC composites) have a wide range of applications in aerospace, nuclear energy, braking systems owing to its excellent mechanical performance. Nevertheless, the hardness, brittleness, heterogeneity, and anisotropy of Cf/SiC composites give rise to difficulties in machining them. In addition, the characterization and formation mechanism of surface damage in the grinding of Cf/SiC composites have not been fully elucidated. The purpose of this paper is to provide a characterization method for surface damage of Cf/SiC composites and an evaluation index for surface edge chipping damage (SECD) through conventional scratching (CS) / ultrasonic vibration assisted scratching (UVAS) tests with single abrasive. Towards revealing the surface damage behavior of Cf/SiC composites during scratching, as well as the impact of fiber orientation on surface damage. The findings indicate that main forms of surface damage of Cf/SiC composites in single abrasive scratching are fiber breakage, fiber fracture-shedding, fiber fracture, fiber-matrix interface debonding, interface fragmentation, matrix cracking, and matrix microcracks. Further, ultrasonic vibration could help to suppress the SECD, and the SECD factor was smallest when scratching along the perpendicular fiber. Furthermore, the fiber orientation can significantly affect the scratching force and cross-sectional area of scratches on Cf/SiC composites via single abrasive scratching. The tangential scratching force was usually smaller as compared to the normal scratching force, and the cross-sectional area of scratches in UVAS is smaller than that in CS. Based on the above findings, this study elucidates the formation and evolution of surface damage after scratching under different fiber orientations, filling the research gap in surface damage under ultrasonic assisted machining of Cf/SiC composites and providing technical guidance for the machining.

Scribing of surface-braided CFRP with picosecond laser: Thermal damage formation and removal mechanism analysis

Scribing of surface-braided CFRP with picosecond laser: Thermal damage formation and removal mechanism analysis

Analysis of buffer-IPyC separation in TRISO fuel particles

During High Temperature Gas-cooled Reactor (HTGR) operation, and due to the neutron irradiation in the reactor core, damage of the nuclear fuel coating layers occurs. The mechanism of damage formation in the TRISO fuel is explored by the Advanced Gas Reactor (AGR) Fuel Development and Qualification Program, in which the debonding process between coating layers was also investigated. The purpose of this paper is to report simulation results for two models. Firstly, the debonding restricted model, where no gap formation between buffer and IPyC layers is permitted. Secondly, a debonding enabled model, where the gap between those layers is created. The simulations were performed with the Bison code. The inputs of the simulated models are based on data from the AGR-1 experiment. The research included simulations on spherical and aspherical fuel types. The simulations match results obtained by the AGR-1 experiment, which as such shows that the Bison code is a good computational method for simulating the behavior of the gap between buffer and IPyC layers in TRISO fuel. Based on the irradiation experiments, and the Bison simulations, it was concluded that the most common scenario is a gap formation along the buffer-IPyC interface, while the least possible scenario is the situation where there is no gap formation at the buffer-IPyC junction. The computational results confirmed that the sphericity of the fuel influences the thickness of the gap that occurs at the buffer-IPyC junction, in a way that with increasing aspect ratio the gap thickness increases. In addition, the fuel sphericity does not influence the Weibull failure probability. The results obtained for spherical and aspherical fuel are nearly identical.

Main mechanisms of secondary ischemic brain damage formation in case of craniocerebral injury

To systematize the mechanisms of formation and morphology of secondary ischemic brain damage, formed in the case of craniocerebral injury. A literature review devoted to the study of formation mechanisms of secondary ischemic brain damage in craniocerebral injury was conducted. The secondary sequential and secondary long-term ischemic brain damage in the posttraumatic period, as well as intracranial and extracranial factors that contribute to their occurrence and progression, were considered. Analysis of the literature has shown that primary lesions occurring at the time of head injury must be differentiated from sequential and long-term secondary ischemic changes in different brain structures.

Study on the removal mechanism and milling quality of helical milling hole of SiCp/Al composites

SiCp/Al composites have been widely used in the aviation field due to their excellent properties such as high strength and good wear resistance, but there are still some problems in their hole-making, such as unclear helical milling removal mechanism and poor hole quality. In this paper, the removal mechanism of SiCp/Al composites in helical milling was analyzed by finite element simulation and a three-factor four-level single-factor test. Then, the effect of process parameters on the surface quality of the hole wall is analyzed by a single-factor test. Finally, the formation mechanism of orifice damage and the influence of process parameters on the quality of the orifice edge are analyzed. The results show that in the helical milling process of SiCp/Al composites, the SiC particles are mainly broken and some fall off. Partial tearing of the aluminum matrix occurs. The quality of the hole wall and orifice becomes better with the increase of spindle speed, and worse with the increase of pitch. The revolution speed has a negative effect on the surface quality of the hole wall and a positive effect on the outlet quality. After the spindle speed increased from 500 r/min to 2000 r/min, the surface roughness decreased by 17.13 %. The surface roughness increased by 68.86 % when the pitch increased from 0.1 mm to 0.4 mm. The surface roughness increased by 9.1 % when the spindle speed increased from 30 r/min to 60 r/min. This paper can provide an important reference for SiCp/Al composites with high efficiency and low damage.

Polytypic transformation behavior from 4H-SiC to 3C-SiC during high-speed scratching of single crystalline silicon carbide

The phase transformation behavior and associated mechanism of 4H-SiC induced by dynamic processing at room temperature conditions can be investigated with high-speed scratching tests. A dedicated high-speed scratching setup is developed to achieve the speed range over 10 m/s to 30 m/s while microscopic detection is performed to study the microstructural alteration of 4H–SiC. Raman spectra analyses indicate that the polytypic transformation from 4H to 3C occurs during high-speed scratching of single crystalline silicon carbide. Transmission electron microscopy demonstrates a shift in the stacking order of the atomic layers to face-centered cubic at the subsurface of the scratched groove, which reveals the formation mechanism of 3C-SiC. Furthermore, the 4H to 3C polytypic transformation exhibits a sensitive scratching speed correlation. The research can enhance the fundamental understanding of the mechanisms of damage formation during manufacturing of 4H-SiC components and provide g guidance for high-quality processing of 4H-SiC crystals.

Study of subsurface damage during nano-grinding of B3-GaN using molecular dynamics simulations

The mechanism of subsurface damage formation during zinc blende gallium nitride (B3-GaN) nano-grinding was investigated using molecular dynamics (MD). The effects of grinding depth and abrasive radius on the grinding force, temperature, potential energy, phase transition, dislocations, the average coefficient of friction (COF), material removal rate (MRR) and subsurface damage were systematically investigated. The results show that dislocations, amorphization and wurtzite (B4) phase transitions are the primary defects present in the subsurface damage layer. Dislocation nucleation and proliferation are the main mechanisms aggravating the subsurface damage, and the 1/2<110> perfect dislocation along the <110> slip direction predominates in the dislocation. Grinding forces, temperature, potential energy, amorphous atoms, B4 phase atoms and dislocations increase with increasing grinding depth, exacerbating the subsurface damage of B3-GaN. As the abrasive radius increases, the amorphous atoms increase and then decrease, with the B4 phase atoms gradually reducing. The rest of the above parameters increase gradually, exacerbating the subsurface damage of B3-GaN. Furthermore, a smaller grinding depth and abrasive radius result in better machining accuracy, but decrease MRR. A technical reference for the ultra-precise and low-damage processing of B3-GaN can be provided by this study.

Support stiffness effects on damage behavior of thin-walled composite interference-fit joints in the installation

Interference installation-induced local interface damage becomes the source of bearing failure in service, which severely restricts the reliable application of composite interference-fit joints. To this end, support stiffness effects on interface damage behavior of thin-walled composite interference-fit joints in the installation was systematically investigated in this paper. The mechanical response and interface damage behavior of the joints were evaluated and compared by interference installation experiments and scanning electron microscopy (SEM). The effects of different support stiffness and lap type on the pressing-in load and interface damage were analyzed. Damage formation mechanism and suppression strategy during installation were discussed. Results show that the weaker the support stiffness is, the greater the bending degree caused by the bottom cantilever is, and the more severe the corresponding interface damage is. Increasing the number of laminated plates only increases the value of the pressing-in load, and has a very limited effect on the interface damage state. To reduce the interface damage of the joints in the installation, in addition to maintain the best interference-fit, keep a considerable value on the bottom support stiffness is also very necessary.

Characteristics of atomic removal and mechanism of damage formation in vibration-assisted nano cutting of copper-nickel alloy

Vibration-assisted machining technology can effectively improve the quality and efficiency of nano cutting, but the characteristics of atomic removal and the mechanism of damage formation have not been systematically studied. In this paper, copper-nickel alloy material is taken as an example. The characteristics of vibration-assisted nano cutting and the plastic deformation behavior of materials were revealed by molecular dynamics simulation. The simulation results show that vibration-assisted nano cutting reduces tangential force, lateral force, and total force, strengthens the anisotropy of atomic motion, and causes greater displacement and removal of Cu/Ni atoms. The intermittent contact is beneficial for the elastic recovery of workpiece atoms, releasing internal stress and atomic strain, reducing the depth of damage and the length of dislocation lines. The difference in surface/subsurface damage to the workpiece is relatively small with an amplitude of 1 Å. With amplitudes of 3 Å and 5 Å, and as the frequency increases, the complete lattice structure is destroyed, resulting in a significant decrease in the number of FCC structural atoms and RDF peak. However, an appropriate increase in frequency can increase the removal of Cu/Ni atoms, improve the topological structure, and reduce RMS. The HCP and BCC structural atoms affect the generation of dislocation lines, with an amplitude of 3 Å and a frequency of 7.5 GHz, achieving the minimum damage depth and dislocation line length. Excessive amplitude of 10 Å results in irreversibly severe damage to the surface/sub-surface of the workpiece. This study will provide a new approach for optimizing vibration-assisted nano-cutting technology and achieving low-damage nano cutting of alloy materials.

Formation mechanism of outlet damage in interlaminar drilling of CFRP

Formation mechanism of outlet damage in interlaminar drilling of CFRP

Abrasive machining induced surface layer damage behavior and formation mechanism of monocrystalline β-Ga2O3: A comparative study of nanoindentation and nanogrinding

Beta-phase gallium oxide (β-Ga2O3) has garnered significant attention in recent years as an ultra-wide bandgap semiconductor material. However, its surface layer damage behavior and machining deformation mechanism remain poorly understood. In this work, a systematic comparative study was conducted through nanoindentation and nanogrinding for monocrystalline β-Ga2O3 (−201) crystal plane. Transmission electron microscopy is employed as the primary characterization method. The results show that the microstructural evolution patterns of monocrystalline β-Ga2O3 can be categorized into four stages, i.e. stacking faults, twins, slip bands, and cleavage cracks are observed sequentially. According to the tests results, subsurface damage diagram models based on nanoindentation and nanogrinding are established, both of which exhibit the above evolution patterns as the indentation depth and grit depth of cut increases. However, there are some differences. In the nanogrinding process, nanocrystals and amorphous layers were found near the ground surface, which are related to the high strain rate grinding conditions and the unique material properties of monocrystalline β-Ga2O3 with low stacking fault energy. The results in this work contribute to an enhanced understanding of the deformation characteristics of monocrystalline β-Ga2O3 at macro and micro scales, while offering valuable insights for achieving damage control in ultra-precision machining processes.

Damage evolution and crystalline orientation effects in ultrafast laser micro/nano processing of single-crystal diamond

Single-crystal diamond is a typical difficult-to-machine material because of its extreme hardness and high brittleness. Compared with traditional machining techniques, ultrafast laser is believed to enable materials processing with high efficiency, high quality and high spatial resolution. To understand the formation mechanism and crystalline orientation effects of damage in ultrafast laser processing diamond, single-path scans were performed in different crystal directions, and groove shape, surface morphology, subsurface damage, phase transformation, and laser-induced periodic surface structure (LIPSS) were systematically analyzed. The experimental results illustrate that the damage evolution can be divided into three different stages according to the pulse number, named weak ablation stage, severe cracking stage, and severe phase transformation stage. Crystal orientation significantly affects the groove shapes, cracks, and phase transformation, and these differences are related to the cleavage energy and atomic rearrangement energy of the crystal plane deposited by the laser energy during processing. At low pulse numbers, the surface graphitization is initiated easier along the <110> direction, which makes the absorption rate of laser energy locally enhanced, further driving the anisotropy of the processing damage at moderate and high pulse numbers. This work provides a new perspective on ultrafast laser processing of single-crystal diamond, which is crucial for ultra-precision and low-damage fabrication of diamond-based functional micro/nano devices.

Effect of tool wear on machining quality in milling Cf/SiC composites with PCD tool

Carbon fiber reinforced silicon carbide ceramic matrix (Cf/SiC) composites have great application potential in aerospace. But their high hardness and anisotropy cause rapid tool wear during machining, which affects machining quality and efficiency. However, tool wear mechanisms in milling Cf/SiC composites are still unclear. There is a lack of research on the relationship between tool wear and cutting performance. In this paper, milling experiments on 2.5D Cf/SiC composites were conducted using polycrystalline diamond (PCD) cutters. The tool wear mechanisms and effect of tool wear on surface roughness, milling force, burr damage, surface microstructure and chips were explored. The results show that abrasive wear caused by chips continuously scraping tool material and diamond particle fragmentation and falling off caused by sprouting and expansion of cracks inside grain were primary causes of tool failure. The formation mechanism of burr damage was analyzed. It was proved that the peak radius of cutting edge Rpeak and flank wear VB could reflect cutting capabilities. It was found that increasing flank wear had regrinding effects on the cutting edge, which affects the peak radius. The degree of burr damage was related to these two parameters. Tool wear changed the surface formation mechanism. Before tool wear, carbon fibers were primarily removed through the micro-brittle fracture, with low surface roughness. The flank face and chips scratched the workpiece like abrasive grains after tool wear, leaving scratches on the surface and increasing surface roughness from 1.27 μm to 2.25 μm.